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Light Full-Node Mode#

Overview#

This mode uses a 2-party authenticated dynamic dictionary built on top of the UTXO set. A light-fullnode only holds the root digest of the dictionary and checks full blocks or a suffix of the blockchain, depending on the setting. It uses AD-transformations to get a new digest from an old one and checks all transactions, but only stores a single digest.

Getting Started#

It's possible to run the node in this light mode using the stateType variable.

Below is a sample ergo.conf for a light node (no UTXO, checking and storing only last 2880 blocks using the blocksToKeep variable

ergo {
  node {
    stateType = "digest" # default is 'utxo'
    blocksToKeep = 2880
    mining = false
  }
}

scorex {
 restApi {
    # Hex-encoded Blake2b256 hash of an API key. Should be 64-chars long Base16 string.
    apiKeyHash = "6ed54addddaf10fe8fcda330bd443a57914fbce38a9fa27248b07e361cc76a41"
  }
}

Technical Workflow#

It checks all the full blocks, or some suffix of the full blockchain, depending on the setting, thus starting from a trusted pre-genesis digest or some digest in the blockchain.

A light-fullnode uses AD-transformations (authenticated dictionary transformations) block section containing batch-proof for UTXO transformations to get a new digest from an old one. It also checks all the transactions but does not store anything but a single digest.

Details can be found in this paper.

Additional settings:

  • depth - from which block in the past to checktransactions (if 0, then go from genesis).
  • additional-checks - light-full node trusts the previous digest and checks current digest validity by using the previous one as well as AD-transformations.
  • additional-depth - depth to start additional checks from.

Steps:

  1. Send ErgoSyncInfo message to connected peers.
  2. Get a response with an INV message containing the ids of blocks, better than our best block.
  3. Request headers for all ids from 2.
  4. On receiving Header:
if(History.apply(header).isSuccess) {
    if(!(localScore == networkScore)) GOTO 1
    else GOTO 5
    } else {
    blacklist peer
    }
  1. Request BlockTransactions and ADProofs starting from BlocksToKeep back in History (just one last header after node bootstrapping):
History.lastBestHeaders(BlocksToKeep).foreach { header =>
    send message(GetBlockTransactionsForHeader(header)) to Random full node
    send message(GetAdProofsHeader(header)) to Random full node
    }
  1. On receiving modifier BlockTransactions or ADProofs:
if(History.apply(modifier) == Success(ProgressInfo)) {
    /* TODO if history now contains both ADProofs and BlockTransactions,
    it should return ProgressInfo with both of them. Otherwise,
    it should return an empty ProgressInfo */
if(State().apply(ProgressInfo) == Success((newState, ADProofs)))
{
if("mode"=="pruned-full") drop BlockTransactions and ADProofs older than BlocksToKeep
}
else {
            /*Drop Header from history because its transaction sequence is not valid*/
            History.drop(BlockTransactions.headerId)
        }
    }